text: /*
   * Copyright (C) 2016 Apple Inc. All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   *
   * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
   * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
   * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
   * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
   * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
   * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
   * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
   * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
   * THE POSSIBILITY OF SUCH DAMAGE.
   */
  
  #pragma once
  
  #if ENABLE(CSS_SCROLL_SNAP)
  
  #include "AxisScrollSnapOffsets.h"
  #include "PlatformWheelEvent.h"
  #include "ScrollTypes.h"
  #include <wtf/Optional.h>
  #include <wtf/Seconds.h>
  
  namespace WebCore {
  
  class FloatPoint;
  class FloatSize;
  
  class ScrollingMomentumCalculator {
  public:
      ScrollingMomentumCalculator(const FloatSize& viewportSize, const FloatSize& contentSize, const FloatPoint& initialOffset, const FloatSize& initialDelta, const FloatSize& initialVelocity);
      static std::unique_ptr<ScrollingMomentumCalculator> create(const FloatSize& viewportSize, const FloatSize& contentSize, const FloatPoint& initialOffset, const FloatSize& initialDelta, const FloatSize& initialVelocity);
      WEBCORE_EXPORT static void setPlatformMomentumScrollingPredictionEnabled(bool);
      virtual ~ScrollingMomentumCalculator() { }
  
      virtual FloatPoint scrollOffsetAfterElapsedTime(Seconds) = 0;
      virtual Seconds animationDuration() = 0;
      virtual FloatSize predictedDestinationOffset();
      void setRetargetedScrollOffset(const FloatSize&);
  
  protected:
      const FloatSize& retargetedScrollOffset() const { return m_retargetedScrollOffset.value(); }
      virtual void retargetedScrollOffsetDidChange() { }
  
      FloatSize m_initialDelta;
      FloatSize m_initialVelocity;
      FloatSize m_initialScrollOffset;
      FloatSize m_viewportSize;
      FloatSize m_contentSize;
  
  private:
      std::optional<FloatSize> m_retargetedScrollOffset;
  };
  
  class BasicScrollingMomentumCalculator final : public ScrollingMomentumCalculator {
  public:
      BasicScrollingMomentumCalculator(const FloatSize& viewportSize, const FloatSize& contentSize, const FloatPoint& initialOffset, const FloatSize& initialDelta, const FloatSize& initialVelocity);
  
  private:
      FloatPoint scrollOffsetAfterElapsedTime(Seconds) final;
      Seconds animationDuration() final;
      void initializeInterpolationCoefficientsIfNecessary();
      void initializeSnapProgressCurve();
      float animationProgressAfterElapsedTime(Seconds) const;
      FloatSize linearlyInterpolatedOffsetAtProgress(float progress);
      FloatSize cubicallyInterpolatedOffsetAtProgress(float progress) const;
  
      float m_snapAnimationCurveMagnitude { 0 };
      float m_snapAnimationDecayFactor { 0 };
      FloatSize m_snapAnimationCurveCoefficients[4] { };
      bool m_forceLinearAnimationCurve { false };
      bool m_momentumCalculatorRequiresInitialization { true };
      std::optional<FloatSize> m_predictedDestinationOffset;
  };
  
  } // namespace WebCore
  
  #endif // ENABLE(CSS_SCROLL_SNAP)
  